Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$30.50	9.772%	$33.4805	$33.48	$33.50	$33.50
Purchase #2	$84.71	9.629%	$92.8667	$92.87	$92.85	$92.90
Purchase #3	$186.64	6.301%	$198.4002	$198.40	$198.40	$198.40
Purchase #4	$159.93	5.220%	$168.2783	$168.28	$168.30	$168.30
Purchase #5	$100.37	11.414%	$111.8262	$111.83	$111.85	$111.80
Purchase #6	$99.63	11.836%	$111.4222	$111.42	$111.40	$111.40
Purchase #7	$87.56	13.608%	$99.4752	$99.48	$99.50	$99.50
7 purchase totals =	$749.34		$815.7493	$815.76	$815.80	$815.80